This is a new application requesting five years of funding for studies aimed at understanding the diversity of fibrillary changes in Alzheimer's disease (AD) and certain other neurodegenerative disorders (corticobasal degeneration, Pick's disease, progressive supranuclear palsy). In AD, a common component of pathological lesions are paired helical filaments (PHF), abnormal twisted filaments composed of hyperphosphorylated tau proteins (PHF-tau). Abnormal tau-immunoreactive filaments accumulate also in other neurodegenerative disorders, yet ultrastructural appearances of these filaments are unique to each disease and differ from that in AD. Tau abnormalities have not yet been described in Diffuse Lewy body disease, which is also included in our studies. In this proposal, we will investigate whether the specific isoform composition of filament- associated tau and/or degree of phosphorylation are important factors responsible for the unique ultrastructural features of abnormal filaments. We hypothesize that tau incorporated into filaments either lacks or has low abundance of those isoforms which contain sequences encoded by exons 2, 3 and 10 of the tau gene and whose expression is developmentally regulated. In our comparative studies we will use antibodies against tau synthetic peptides as isoform-specific probes and employ multiple biochemical as well as immunochemical methodologies including immunoelectron microscopy. We hypothesize that the molecular and biochemical diversity of filament-associated tau may be indicative of the selective degeneration of different brain cells, either glial or neuronal. Therefore, we plan to examine the regional involvement of brain white and gray matter in these disorders, with emphasis on comparisons of tau abnormalities and content of normal tau, and use isolated brain fractions enriched for either neuronal or glial cells: astrocytes and/or oligodendrocytes. Primary tissue cultures of glial cells will be established to demonstrate under variety of conditions whether isoform composition of tau expressed in vitro corresponds to that of filament- associated tau in vivo. Furthermore, in this proposal we hypothesize that the diversity of tau may be an important regulatory factor in binding to Ca2+/calmodulin (CaM) and S100beta, which results in destabilization of microtubules in neuronal or glial cells, respectively. In AD and other neurodegenerative disorders, defective Ca2+ homeostasis and/or expression of CaM or S100 genes may result in destabilization of microtubules, accumulation of unassembled hyperphosphorylated tau and formation of pathological filaments in a specific population of affected cells.